I. The physical condition of infants and young children after cardiovascular surgery, the role and significance of nutritional support: 1. 4.Neonates and young children have very low energy reserves, poor glycogen allogenesis and weak digestive capacity; 5.Poorly developed respiratory muscles lead to poor cough reflex, storage of secretions, poor respiratory capacity and sputum removal, and many respiratory complications. In view of the above reasons, pre- and postoperative malnutrition can lead to tissue edema, poor wound healing, many respiratory complications, reduced wound healing and anti-infection ability of the child, and can cause renal failure and heart failure. Therefore, pay attention to strengthen preoperative and postoperative nutritional support, it can be said that poor nutrition can directly affect postoperative recovery. The most simple and clinically meaningful is to measure the weight and length, head circumference, chest circumference, inner diameter of the upper arm, subcutaneous fat thickness and other indicators; 2, biochemical measurement indicators are total protein, albumin, hemoglobin, creatinine, total lymphocytes, white blood cell count, etc.; 3, the clinical manifestations of children with poor nutrition are mostly The clinical manifestations of poorly nourished children are mostly lethargy, indifference, poor skin elasticity, sunken fontanel and other symptoms. The physiological characteristics of newborns and infants: The stomach of small infants is horizontal, and the pancreatic tone of infants is low, so vomiting and milk spillage can easily occur. In addition, the gastrointestinal tract is immature, the digestive enzyme activity is low, the number is small, easy to occur indigestion, diarrhea, so breastfeeding should be encouraged, because it best meets the infant’s digestive capacity and nutritional requirements. The metabolism of infants and young children is high, so in addition to maintaining body consumption and tissue repair, it is more important to supply growth and development. Infants and young children grow rapidly and have a high basal metabolic rate, which is influenced by many factors, such as an increase in body temperature by 1℃ and a 13% increase in basal metabolic rate. The basal metabolic rate of infants and young children is calculated as 2 (Kcal) × 24hr × kg. The infant fluid intake should be calculated per square meter of body surface area or per kilogram of body weight. The total fluid intake should be calculated in milliliters. The total intake includes all kinds of intravenous drugs, flushing fluid, and oral volume; the total output includes non-significant fluid loss, drainage, and urine volume. The principle of cardiac diuretic therapy in pediatric surgery does not mean blindly controlling the incoming volume, but filtering out excess water and reducing the cardiopulmonary burden while maintaining circulatory stability.